Background. Do pressure dependent tracheal obstructions (PDTO) often seen during bronchoscopy in COPD patients affect pulmonary function tests and breathing symptoms? Method. Model study. A garden hose was compressed from one side to simulate the posterior wall of the trachea bulging into the lumen. For two obstruction lengths - 3 cm and 12 cm, the hose was increasingly compressed in eight steps. Resistance was measured at each step for airflows 1 l/s through 9 l/s, and digital photos of the luminal area were taken which were used by a computer to estimate the cross sectional area reduction and the corresponding distance between the bulging (posterior)and the opposite (anterior) wall (AP-distance).

Patient study. 104 stable COPD patients studied by pulmonary function tests and bronchoscopy. The tracheal obstruction was observed during forced expiration and cough, and the cross sectional area reduction was estimated using the results from the model study.

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Please refer to this study by its ClinicalTrials.gov identifier: NCT01679808